Trans. Nonferrous Met. Soc. China 25(2015) 3827-3833

Reaction pathway led by silicate structure transformation on decomposition of CaSiO₃ in alkali fusion process using NaOH

Chang-ming ZHAO^1,2, Guo-cheng WANG^1,2, Sheng-li LI^1,2, Xin-gang AI^1,2, Zi-rui WANG³, Yu-chun ZHAI³

1. School of Materials and Metallurgy, University of Science and Technology Liaoning, Anshan 114051, China;

2. Key Laboratory of Chemical Metallurgy Engineering of Liaoning Province, Anshan 114051, China;

3. School of Materials and Metallurgy, Northeastern University, Shenyang 110004, China

Received 9 December 2014; accepted 17 June 2015

Abstract: The mechanism of decomposition of calcium inosilicate (CaSiO₃) synthesized through chemical deposition method using analytical reagent NaSiO₃·9H₂O and CaCl₂ during the alkali fusion process using NaOH was investigated by Raman spectroscopy in situ, X-ray diffraction and Fourier transform infrared spectrometer (FTIR). The results show that the tetrahedral silica chains within CaSiO₃ are gradually disrupted and transformed into nesosilicate with the isolated SiO₄ tetrahedra at the beginning of the alkali fusion process. The three intermediates including Ca₂SiO₄, Na₂CaSiO₄ and Na₂SiO₃ appear simultaneously in the decomposition of CaSiO₃, while the final products are Ca(OH)₂ and Na₄SiO₄. It can be concluded that there exist two reaction pathways in the alkali fusion process of CaSiO₃: one is ion exchange, the other is in the main form of the framework structure change of silicate. The reaction pathway is led by silicate structure transformation in the alkali fusion process.

Key words: alkali fusion process; CaSiO₃; intermediate; reaction pathway

1 Introduction

In recent years, several investigations have focused on the utilization of silicon magnesium laterite nickel ore because of the shortage of high-grade nickel sources [1]. The features of silicon magnesium laterite nickel ore are low nickeliferous grade (1%-2%, mass fraction), abundant in associated ores, contents (mass fraction) of magnesium, silicon and calcium of above 30%, easy to form garnierite ((Ni,Mg)SiO₃·nH₂O) and calcium silicate (Ni, Ca)SiO₃·nH₂O), in which various metal ions are embedded in each other. In general, silicate-rich garnierite ores are amenable to pyrometallurgical processes to produce carbon ferro-nickel alloys, while nickel bound within genthite, clay and saprolite ores is processed hydrometallurgically, such as atmospheric acid-leaching and high pressure acid-leaching [2-4]. However, the stable silicate structure cannot be destroyed to release valuable mineral elements efficiently by the traditional pyrometallurgical and hydrometallurgical processes, which means low utilization of valuable elements, high energy consumption and negative environmental impact.

Alkali processing of nickel laterite ore has attracted wide concern recently due to its simple process, low energy consumption and low investment [5-7]. A lot of researches were focused on the optimization of the alkali processing conditions, macrokinetics and pre- desiliconization [8,9]. The alkali-fusion process is an important operation, during which the strong bonds between the metal and silica part within the compound can be disrupted, then the metal atoms are released from the SiO₄ tetrahedral network. Therefore, it can lead to high yield of nickel from the activated clinker by the subsequent acid-leaching process under moderate conditions. However, there have been few reports on the mechanism of alkali activation for the silicate in detail up to now, especially for the intermediates and kinetic pathway of the reactions, although the initial materials and final products are usually known for the related chemical reactions. It is often difficult, if not impossible, to gather materials which represent reaction intermediates.

In the current study, Raman spectra in situ during the alkali treatment process were used to identify the presence of the intermediates of the reactions, and reveal the reaction pathway to the alkali treatment process. Furthermore, X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FTIR) analyses were used to identify the changes of mineral phase structure in alkali treatment process. Here, we adopted the synthetic calcium inosilicate (CaSiO₃) instead of the natural garnierite, and examined binding changes and transient phase transformations occurring in the alkali-fusion by Raman spectroscopy in situ and X-ray diffraction analyses. Normally, in garnierite, CaSiO₃ is the major composition, in which minor nickel substitutes calcium. The general formula (Ca_1-xNi_x)SiO₃ of their solid solutions are isomorphous. The mechanism of (Ca,Ni)SiO₃ decomposition during the alkali fusion process could be analogous to the formation of CaSiO₃. The typical Raman spectra with distinct sharp peaks of the colorless CaSiO₃ can be facilely collected, which is another important reason for CaSiO₃ to serve as the subject of investigation in this study instead of the natural dark green garnierite.

2 Experimental

2.1 Synthesis of CaSiO₃

The experimental materials including NaOH, Na₂SiO₃·9H₂O and CaCl₂ were all analytical reagent and water was distilled water. The CaSiO₃ colloid precursor was synthesized by a chemical precipitation method using the mixed solution of Na₂SiO₃·9H₂O and CaCl₂ with uniform molar concentration at room temperature. The colloid precursor was further calcined to form solid CaSiO₃ in a muffle furnace.

2.2 Decomposition of CaSiO₃ by melting NaOH

The decomposition experiments of CaSiO₃ by melting NaOH were carried out in a stainless steel reactor. The reactor was heated with a heating jacket and the reaction temperature was controlled with a KWT type temperature controller. A nickel chromium-nickel silicon thermocouple was used for temperature measurement with a control precision of ±2 °C. A stirring device and a reflux condenser were on the reactor. The whole reactor was sealed in decomposing CaSiO₃ process by melting NaOH. The device of experimental reactor is shown in Fig. 1. Firstly, the solid NaOH and CaSiO₃ with various NaOH/CaSiO₃ mole ratios were added into the reactor, and heated to a set of temperatures. After the reaction period, the temperature of the reaction system decreased to room temperature. Then, the leaching was done by adding distilled water into the reactor. The leaching solution containing soluble silicate and leaching residue can be separated through centrifugation method.

Fig. 1 Experimental apparatus for decomposing CaSiO₃ process by melting NaOH

2.3 In suit Raman spectroscopy analysis

The alkali fusion process of CaSiO₃ with various mole ratios of NaOH to CaSiO₃ was investigated in the homemade micro-furnace under different operating conditions by Raman spectroscopy in situ. Raman spectra were collected on the Raman spectrometer (Jobin Y’von LABRAM HR800). The pulsed exciting light (355 nm) from a Q-switch pulsed THG-Nd: YAG laser was focused by an Olympus BH-2 microscope, and the Raman scattering light from the reactants was collected by a Confocal-len system. The spectral resolution was better than 2 cm^-1 and the spatial resolution was about 1 μm. The Raman spectrometer was equipped with the intensive charge-coupled device (ICCD) to investigate the alkali fusion process.

2.4 XRD and FTIR analysis

The cooled clinker of products of the alkali fusion process was washed with tap water at room temperature several times. The undissolved residue was centrifugally separated from the solution and dried at room temperature for subsequent XRD and FTIR analyses. Phase analyses of all the samples were carried out with a D/Max-2500PC X-ray diffractometer with Cu K_α radiation and a Nicolet 380 FTIR spectrometer.

3 Results and discussion

3.1 Structure of synthetic CaSiO₃

The XRD patterns of the CaSiO₃ colloid precursor calcined at 900, 1000 and 1100 °C for 3 h are shown in Fig. 2. The characteristic diffraction peak intensity of the products is enhanced with increasing the calcination temperature. It is demonstrated that the characteristic diffraction peak of the calcination product at 1100 °C is very sharp and has less impurity peaks, which shows that the calcined product is in a good crystalline state. The calcined product phase is found to be CaSiO₃ (JCPDS No.42-547). The SEM image of CaSiO₃ particles including cube and schistose is shown in Fig. 3.

Fig. 2 XRD patterns of CaSiO₃ precursor calcined at different reaction temperatures

Fig. 3 SEM image of CaSiO₃ precursor calcined at 1100 °C for 3 h

Figure 4 shows the FTIR pattern of CaSiO₃ calcined at 1100 °C for 3 h. Previous theory analysis indicated that there exist four major infra vibration modes for the CaSiO₃ lattice structure: symmetric stretching mode of Si—O—Si (725 and 693 cm^-1) [10,11], antisymmetric stretching mode of Si—O—Si (1012 and 936 cm^-1) [12,13], symmetric stretching mode of Si—O_nb (872 cm^-1) and bending of Si—O_nbmode (555 and 436 cm^-1) [14,15].

Fig. 4 FTIR pattern of CaSiO₃ precursor calcined at 1100 °C for 3 h

Fig. 5 Raman spectra of CaSiO₃ at prepared temperatures from 20 to 500 °C

Figure 5 shows the Raman spectra of CaSiO₃ prepared at different temperatures from 20 to 500 °C. All the bands show a minor shift to lower wavenumber with temperature increasing from 20 to 500 °C because of the increase of bond distance between Ca²⁺ and SiO₄^4- tetrahedra. In general, the inosilicates are characterized by the Si—O—Si bending vibration bands between 400 and 750 cm^-1, the Si—O stretching vibration bands (Q_n) between 800 and 1100 cm^-1 and metal—O bending vibration bands below 600 cm^-1. The characteristic peaks of Raman vibration spectrum of CaSiO₃ are all located in the wavenumber range of 200-1200 cm^-1, among which 970 cm^-1 belongs to a symmetric stretching vibration peak of SiO₄^4-, 1044 cm^-1 belongs to an antisymmetric stretching vibration band of SiO₄^4-, 411 and 636 cm^-1 belong to bending vibration mode of Si—O—Si [16,17]. The frequencies of the stretching modes are related to the degree of polymerization of the SiO₄^4- tetrahedral network: the tetrahedra with zero (Q₀), one (Q₁), two (Q₂) and three (Q₃) bridging oxygen atoms are associated with the modes at 850, 900, 950-1000 and 1050-1100 cm^-1, respectively. The wavenumbers of Si—O—Si bending vibration of the prepared CaSiO₃ in current study are at around 411 and 636 cm^-1, while the wavenumbers of Q₂ are 970 and 1044 cm^-1 under ambient conditions. The vibration band below 400 cm^-1 is caused by the large frame vibration with the participation of the cation. The typical Raman spectrum of the prepared CaSiO₃ confirms that it has silica tetrahedra (Q₂), which is branched together by calcium octahedra.

3.2 Silicate structure transformation in alkali fusion process

The alkaline fusion process of the prepared CaSiO₃ using NaOH under different operating conditions was carried out to obtain the details about the alkali fusion process of CaSiO₃, including the presence of the reaction intermediates. The residues from the alkali fusion process followed by water washing were examined by XRD analysis. Figure 6 shows XRD patterns of water-leaching residues from CaSiO₃ after alkali fusion process at 500 °C for 1 h with mole ratios of NaOH to CaSiO₃ being 4:1, 6:1 and 8:1. It can be deduced from the XRD patterns that the structure of CaSiO₃ is decomposed into the nesosilicate (Q₀) Ca₂SiO₄ and Na₂CaSiO₄ and a small quantity of chains (Q₂) Na₂SiO₃, since the phases including Ca₂SiO₄, Na₂CaSiO₄, Na₂SiO₃ and Ca(OH)₂ were detected from the XRD pattern of the residue at a mole ratio of NaOH to CaSiO₃ being 4:1. Excess NaOH could keep reacting with Na₂SiO₃ and Ca₂SiO₄ to form the nesosilicate (Q₀) Na₄SiO₄ and Na₂CaSiO₄ except for the decomposition of CaSiO₃. Furthermore, Ca²⁺ released from the silicate structure and then combined with OH^- to form Ca(OH)₂ because the reaction between NaOH and Ca₂SiO₄ or Na₂CaSiO₄ was promoted with the increase of mole ratio of NaOH to CaSiO₃. Thus, the probable reactions between CaSiO₃ and melting NaOH are as follows:

4CaSiO₃+10NaOH=Ca₂SiO₄+Na₂CaSiO₄+Ca(OH)₂+2Na₄SiO₄+4H₂O  (1)

4CaSiO₃+8NaOH=Ca₂SiO₄+Na₂CaSiO₄+Ca(OH)₂+3NaSiO₃+3H₂O   (2)

Ca₂SiO₄+2NaOH=Na₂CaSiO₄+Ca(OH)₂          (3)

Na₂CaSiO₄+2NaOH=Na₄SiO₄+Ca(OH)₂          (4)

Na₂SiO₃+2NaOH=Na₄SiO₄+H₂O               (5)

Figure 7 shows the FTIR patterns of water-leaching residues from CaSiO₃ after alkali fusion process at 500 °C for 1 h with mole ratios of NaOH to CaSiO₃ being 4:1, 6:1 and 8:1. In the FTIR patterns of reaction mixture, the peaks at 1610-1649 cm^-1 are attributed to the bending vibration mode of H—O—H in combined water, while the peaks at 1428-1446 cm^-1 are attributed to the stretching vibration mode of C—O in CO₃^2- [18]. This indicates that part of molten NaOH can react with CO₂ in ambient air to produce Na₂CO₃.

Fig. 6 XRD patterns of water-leaching residues from CaSiO₃ after alkali fusion process at 500 °C for 1 h with mole ratios of NaOH to MgSiO₃ being 4:1, 6:1 and 8:1

Fig. 7 FTIR patterns of water-leaching residues from CaSiO₃ after alkali fusion process at 500 °C for 1 h with mole ratios of NaOH to CaSiO₃ being 4:1, 6:1 and 8:1

With increasing the mole ratio of NaOH to CaSiO₃, the peaks at 725 and 693 cm^-1 belonging to Si—O—Si symmetric stretching mode disappear [19]. In the mean time, the peaks of Si—O_nb antisymmetric stretching and bending mode appear at about 985 and 610 cm^-1, respectively, which prove that the structure of silicate transforms from Q₂ to Q₀ [20]. XRD analysis shows that the main products of reaction are Ca₂SiO₄ and Na₂CaSiO₄ when mole ratio of NaOH to CaSiO₃ is 4:1. The new antisymmetric stretching mode of Si—O—Si at 716 cm^-1 indicates part silica chain units still remain in reaction mixture while the structure of silicate network varies with the development of reaction. XRD analysis shows that Ca²⁺ is replaced by Na⁺ in Q₂ silicate species when the mole ratio of NaOH to CaSiO₃ is 4:1.

As the NaOH content rises furthermore, the peak of Si—O_nb stretching mode appears at about 870 cm^-1 while one of Si—O—Si antisymmetric stretching modes disappears gradually [21]. This indicates that the remaining Si—O—Si bonds in Na₂SiO₃ lattice are decomposed by NaOH. XRD analysis shows that Na₄SiO₄ (a kind of Q₀ silicate species) appears when the mole ratio of NaOH and CaSiO₃ rises up to 8:1.

The Raman spectra were collected continuously during the alkali fusion process to make references for distinguishing the reaction intermediates by Raman spectroscopy in situ, once the reactants were heated up to different setting temperatures, which rose at the rate of 10 °C/min from room temperature. Figures 8 and 9 display the Raman spectra of the reaction mixture at different temperatures, in which the mole ratios of NaOH to CaSiO₃ are 4:1 and 8:1, respectively.

The intensity of Raman spectrum of the sample diminishes intensely when temperature is 300 °C. Similar phenomena are observed at the Raman spectra of ceria doped by rare-earth cations. In these systems, the distribution of defects in the lattice causes the disappearance of the Raman spectra. This suggests that in a similar way, the ordered defects such as polysynthetic twins happen in the reaction of silicate with NaOH.

Fig. 8 Raman spectra of prepared CaSiO₃ during alkali fusion process as function of elevated temperature at mole ratio of NaOH to CaSiO₃ being 4:1

Fig. 9 Raman spectra of prepared CaSiO₃ during alkali fusion process as function of elevated temperature at mole ratio of NaOH to CaSiO₃ being 8:1

The variations in Raman vibration mode of CaSiO₃ decomposed by alkali with temperature rising are shown in Figs. 8 and 9. In the present work, Raman bands below 400 cm^-1 are assigned to vibrations of the M—O (M=Ca or other metals) bonds and the long-range ordering of the silicate network [22]. The highest wavenumber bands at about 1074 cm^-1 is due to OH^- in NaOH. With the temperature rising, the bending vibration band of CaSiO₃ at 411 cm^–1 shifts to low wavenumber. Previous studies on temperature dependent Raman spectra of inorganic crystals and melts assign similar red shifts to the weakening of the central atom ligand bonding due to volume expansion with temperature rising and the degree of crystal defect in natural materials. This may imply that crystal defect and structural disorders appear in CaSiO₃ lattice in molten alkali at high temperature as the radiation or metamictization does in natural silicate material.

When the mole ratio of NaOH to CaSiO₃ is 4:1, the bands at 970, 1010 and 1039 cm^–1 assigned to Si—O—Si bond of CaSiO₃ diminish at above 300 °C. With the increase of NaOH content, the bands of CaSiO₃ disappear at lower temperature, which indicates that higher OH^- content accelerates the decomposition of CaSiO₃. The vibration bands at 850 cm^-1 attributed to Si—O_nb bonds appear after the bands of CaSiO₃ diminish. These features indicate the chain silicate structure of CaSiO₃ is disrupted by NaOH and isolated silicate species is obtained during the alkali fusion reaction process. With the increase of NaOH content, the vibration band at 850 cm^-1 shifts to 830 cm^-1. This behavior reflects that a lot of cations which bond to SiO₄^4- tetrahedron in Q-species diminish with the loading of NaOH. The XRD analysis proves that Ca₂SiO₄ as an intermediate transforms to Na₂CaSiO₄ during NaOH fusion reaction process.

The appearance of bands at 980 cm^-1 assigned to enstatine phase (Na₂SiO₃) proves that part of SiO₄ tetrahedra polymerize to Q₂ silicate species at the initial stage of reaction [23]. With the increase of temperature, the vibration bands at 807 cm^–1 assigned to the asymmetric stretching vibration of Q₀ in Na₄SiO₄ show that Si—O—Si bonds in Na₂SiO₃ lattice are disrupted by NaOH again. Only the bands assigned to the symmetric stretching vibration can be observed when temperature rises up to 500 °C, which proves that Ca atoms are replaced by Na atoms completely. So, Na₄SiO₄ is obtained as final products.

3.3 Reaction pathway

There exist two reaction pathways in the calcium silicate alkali fusion process: one is ion exchange, the other is in the main form of the framework structure change of silicate. According to the silicate structure transformation in alkali fusion process, the reaction pathway and lattice structure variation of silicate in reaction system are shown in Fig. 10. After the two pathways of parallel structure transformation, CaSiO₃ is changed to the final product Na₄SiO₄. According to the above experimental analysis results of Raman, FTIR and XRD, there exist three intermediate products in the two pathways. They are Ca₂SiO₄, Na₂CaSiO₃ and Na₂SiO₃, respectively. The two pathways are CaSiO₃ → Ca₂SiO₄ → Na₂CaSiO₄ → Na₄SiO₄ and CaSiO₃ → Na₂SiO₃ → Na₄SiO₄ , respectively, which take place simultaneously in alkali fusion process. Based on this finding, it can provide reference to the optimization of NaOH addition by alkaline method in the silicate-laterite-nickel ore process.

Fig. 10 Reaction pathway and structure evolution of silicate

4 Conclusions

1) Combining Raman spectroscopy in situ with the XRD and FTIR analyses can give the decomposition pathway of CaSiO₃ during the alkali fusion process using NaOH.

2) The silica tetrahedral chains within calcium inosilicate (CaSiO₃) are gradually disrupted, and nesosilicates with the isolated tetrahedra are reorganized at the beginning of the alkali fusion process.

3) Ca₂SiO₄, Na₂CaSiO₄ and Na₂SiO₃ are the three intermediates appearing in the decomposition process, however, the final products are Ca(OH)₂ and Na₂SiO₄.

4) There exist two reaction pathways in the calcium silicate alkali fusion process: one is ion exchange, the other is in the main form of the framework structure change of silicate.

References

[1] ZHAO Chang-ming, ZHAI Yu-chun. Leaching behavior mechanism of Mg₂SiO₄ in high NaOH content system [J]. The Chinese Journal of Nonferrous Metals, 2013, 23(6): 1764-1768. (in Chinese)

[2] SHEN Xiao-yi, SHAO Hong-mei, WANG Jia-dong, ZHAI Yu-chun. Preparation of ammonium jarosite from clinker digestion solution of nickel oxide ore roasted using (NH₄)₂SO₄ [J]. Transactions of Nonferrous Metals Society of China, 2013, 23(11): 3434-3439.

[3] KAR B B, SWAMY Y V, MURTHY B V R. Design of experiments to study the extraction of nickel from lateriticore by sulphatization using sulphuric acid [J]. Hydrometallurgy, 2006, 56(3): 387-394.

[4] SENANAYAKE G, CHILDS J, AKERSTROM B D, PUGAEV D. Reductive acid leaching of laterite and metal oxides—A review with new data for Fe(Ni,Co)OOH and a limonitic ore [J]. Hydrometallurgy, 2011, 110(1): 13-32.

[5] GUO Qiang,QU Jing-kui,QI Tao, WEI Guang-ye, HAN Bing-bing. Activation pretreatment of limonitic laterite ores by alkali-roasting method using sodium carbonate [J]. Minerals Engineering, 2011, 24(8): 825-832.

[6] GUO Qiang,QU Jing-kui,HAN Bing-bing,WEI Guang-ye,QI Tao. Dechromization kinetics of limonitic laterite ores by alkali-roasting method using sodium hydroxide [J]. Advanced Materials Research, 2011, 233-235(5): 798-804.

[7] GUO Qiang,QU Jing-kui,QI Tao, WEI Guang-ye,HAN Bing-bing. Activation pretreatment of limonitic laterite ores by alkali-roasting using NaOH [J]. International Journal of Minerals Metallurgy and Materials, 2012, 19(2): 100-105.

[8] ABDELKADER A M, DAHER A, EL-KASHEF E. Novel decomposition method for zircon [J]. Journal of Alloys and Compounds, 2008, 460(1-2): 577-580.

[9] HIDETSUGU M. Extraction of silicon dioxide from waste colored glasses by alkali fusion using sodium hydroxide [J]. Journal of the Ceramic Society of Japan, 2003, 111: 376-381.

[10] SANDHU A K, SINGH S, PANDEY O P. Neutron irradiation effects on optical and structural properties of silicate glasses [J]. Materials Chemistry and Physics, 2009, 115(12): 783-788.

[11] M, PALUSZKIEWICZ C. The structural role of alkaline earth ions in oxyfluoride aluminosilicate glasses-infrared spectroscopy study [J]. Vibrational Spectroscopy, 2008, 48(2): 246-250.

[12] FATHI M H, KHARAZIHA M. The effect of fluorine ion on fabrication of nanostructure for sterite during mechanochemical synthesis [J]. Journal of Alloys and Compounds, 2009, 472(1-2): 540-545.

[13] RAYMOND J. Infrared spectra of olivine polymorphs: α, β phase and spinel [J]. PhysicsandChemistryofMinerals, 1980(5): 327-339.

[14] HUANG S P, YOU J P, JIANG G C, YOSHIDA F, XU K D. A molecular dynamics simulation of CaSiO₃ melt under an electric field [J]. Chinese Physics Letters, 2000, 17(4): 279-281.

[15] SANG-HEON S,KRYSTLE C. Compositional dependence of structural transition pressures in amorphous phases with mantle- related compositions [J]. Earth and Planetary Science Letters, 2009, 283(1-4): 174-180.

[16] CHEN He-sheng,SUN Zhen-ya, SHAO Jing-chang. Investigation on FT-IR spectroscopy for eight different sources of SiO₂ [J]. Bulletin of the Chinese Ceramic Society, 2011, 30(4): 934-937. (in Chinese)

[17] CHARLES A, GEIGER. A low-temperature IR spectroscopic investigation of the H₂O molecules in the zeolite mesolite [J]. European Journal of Mineralogy, 2012, 24(1): 439-445.

[18] DALBY N K, KING P L. A new approach to determine and quantify structural units in silicate glasses using micro-reflectance Fourier-transform infrared spectroscopy [J]. American Mineralogist, 2006, 91: 1783-1793.

[19] KATIE G, OREB J B. Chemical bonding of ultra low expansion glass substrates with aqueous NaOH solution [J]. Materials Chemistry and Physics, 2011, 130(3): 577-582.

[20] ROY B N. Assessment of the CaO-Al₂O₃ system [J]. JournaloftheAmerican Ceramic Society, 1990, 73: 15-23.

[21] BOWEY J E, MORLOK A, M, GRADY M. 2-16 μm spectroscopy of micron-sized enstatite (Mg,Fe)₂Si₂O₆ silicates from primitive chondritic meteorites [J]. Monthly Notices of the Royal Astronomical Society, 2007, 376(3): 1367-1374.

[22] WALRAFEN G E, DOUGLASA R T W. Raman spectra from very concentrated aqueous NaOH and from wet and dry solid and anhydrous molten, LiOH, NaOH, and KOH [J]. The Journal of Chemical Physics, 2006, 124(1): 114504-114518.

[23] LIN C C, CHEN S F, LIU L G.Anionic structure and elasticity of Na₂O-MgO-SiO₂ glasses [J]. Journal of Non-crystalline Solids, 2007, 353: 413-425.

NaOH碱熔分解CaSiO₃过程中导致硅酸盐结构转变的反应路径

赵昌明^1,2，王国承^1,2，李胜利^1,2，艾新港^1,2，王子睿³，翟玉春³

1. 辽宁科技大学 材料与冶金学院，鞍山 114051；

2. 辽宁省化学与冶金工程重点实验室，鞍山 114051；

3. 东北大学 材料与冶金学院，沈阳 110004

摘  要：以NaSiO₃·9H₂O和CaCl₂为原料，通过化学沉积法合成链状硅酸盐(CaSiO₃)。采用拉曼光谱、X射线衍射和红外光谱研究其在NaOH碱熔过程中的分解机制。结果表明，CaSiO₃在碱熔过程中链状结构的硅氧四面体结构逐渐断裂、转变生成岛状结构的硅氧四面体。CaSiO₃分解过程中同时生成3种中间体：Ca₂SiO₄, Na₂CaSiO₄和Na₂SiO₃，最终产物是Ca(OH)₂和 Na₄SiO₄。因此，CaSiO₃在NaOH碱熔融反应过程中存在两条反应途径，分别以离子交换和硅酸盐骨架结构改变为主要形式，碱熔过程中硅酸盐结构的变化贯穿于整个反应过程。

关键词：碱熔过程；CaSiO₃；中间体；反应路径

(Edited by Wei-ping CHEN)

Foundation item: Project (20112120120003) supported by the Science and Technology Projects of Ministry of Education of China; Project (L2014120) supported by the Educational Commission of Liaoning Province, China

Corresponding author: Guo-cheng WANG; Tel/Fax: +86-412-5929534; E-mail: wangguocheng770921@ustl.edu.cn

DOI: 10.1016/S1003-6326(15)64027-4